1. Field of the Invention
The present invention relates to a printed circuit board having an embedded thin-film capacitor, and a method of manufacturing the same. More specifically, the present invention relates to a printed circuit board having an embedded thin-film capacitor, which is capable of improving product reliability and reducing a product production cost by controlling the electrode surface roughness via formation of an upper electrode of a thin film capacitor using an electroplating method, and a method of manufacturing the same.
2. Description of the Related Art
Recently, an ongoing trend toward higher performance of electronic equipment has led to an increasing market demand for passive devices having a high-integration degree. However, various passive devices, which have been conventionally mounted and arranged on printed circuit boards (PCBs), are generally recognized as a significant obstacle against miniaturization of such electronic equipment. In particular, speeding trends toward the development of embedded systems of semiconductor active devices and increasing numbers of input/output terminals of the devices result in a need to secure the arrangement space for a higher number of passive devices disposed around active devices. However, it is not easy to solve such problems associated with securing of the arrangement space.
As typical examples of passive devices, there are capacitors. Such capacitors require an optimal disposition to decrease a high frequency-induced inductance as they seek higher frequency applications in an operating frequency thereof. For example, decoupling capacitors, which have been used for a stable supply of an electric power, require the disposition thereof in the closest proximity of the input terminal in order to reduce a high frequency-induced inductance.
In order to keep up with increasing demands for the downsizing and higher frequency applications of semiconductor devices including the decoupling capacitor, various types of multi-layer ceramic capacitors (MLCCs) having low equivalent series inductance (Low ESL) have been actively developed. Nonetheless, conventional MLCCs, which are discrete devices, have suffered from fundamental limitations and difficulties to overcome the above-mentioned problems. These capacitors are widely used as a device of an electric circuit. Therefore, if they can be embedded within electric circuit boards, it is possible to effectively reduce a required area of the circuit board. Recently, to investigate the feasibility of such an idea, a great deal of research and study has been actively focused on the development of an embedded capacitor.
The embedded capacitor is embedded in PCBs which have been used in memory cards, PC main boards and various RF modules, and therefore its application may lead to a remarkable reduction of a product size. Further, owing to a feasible disposition of the embedded capacitor in the proximity of the input terminal of the active device, it is advantageously possible to significantly reduce a high frequency-induced inductance by minimizing a length of a lead wire connected to the capacitor via such an optimal disposition of the embedded capacitor.
As an example of such an embedded capacitor, mention may be made of a patent invention disclosed in U.S. Pat. No. 6,818,469. According to this art, a printed circuit board 10 having a conventional thin-film capacitor embedded therein, as shown in FIG. 1, has suggested an embedded thin film capacitor including an insulating substrate 11a, a lower electrode 13 formed on the insulating substrate 11a, a dielectric thin film 15 formed on the lower electrode 13, and an upper electrode 17 formed on the dielectric thin film 15.
On the other hand, upon manufacturing of such a conventional thin film capacitor, the upper and lower electrodes of the capacitor are formed by application of a physical vapor deposition (PVD) method such as sputtering, e-beam evaporation or the like, which suffers from a difficulty to obtain a desired thickness of the electrode in terms of cost. Further, the electrode, formed through such a PVD method, typically has a surface roughness (Ra) of less than 100 nm. Hence, where the insulating substrate 11b such as a prepreg is pressure-deposited on the top of the upper electrode 17 during a subsequent process, the delamination 19 between the upper electrode 17 and the thus-deposited insulating substrate 11b may occur, which consequently makes it difficult to apply such a thin film capacitor to an organic circuit board.
Further, disadvantageously, such a conventional thin film capacitor disclosed in the above US patent cannot be applied to manufacturing of a printed circuit board (PCB) which is a polymer composite-based insulating substrate, because heat treatment at a temperature of 400° C. following the formation of the dielectric film is carried out so as to improve a dielectric constant.